512 lines
11 KiB
HTML
512 lines
11 KiB
HTML
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<!DOCTYPE HTML>
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<HTML LANG="en-us"
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><HEAD
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><TITLE
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>*read-suppress* | Common Lisp Nova Spec</TITLE
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><META CHARSET="US-ASCII"
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><LINK REL="canonical" HREF="v_read-suppress.html"
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><LINK REL="next" HREF="v_readtable.html" TYPE="text/html" TITLE="*readtable*"
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><LINK REL="prev" HREF="v_read-eval.html" TYPE="text/html" TITLE="*read-eval*"
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><LINK REL="up" HREF="23_2_Reader_Dictionary.html" TYPE="text/html" TITLE="23.2 Reader Dictionary"
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><LINK REL="start" HREF="index.html" TYPE="text/html" TITLE="Common Lisp Nova Spec"
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><META NAME="VIEWPORT" CONTENT="width=device-width, initial-scale=1.0"
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><LINK REL="STYLESHEET" HREF="dpans.css%3F3909942064.css"
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><SCRIPT SRC="dpans.js%3F3909942064"
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></SCRIPT
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><SCRIPT SRC="apropos.js%3F3909942064"
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></SCRIPT
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></HEAD
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><BODY
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><DIV
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><DIV CLASS="topnav"
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><DIV CLASS="breadcrumb"
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><SPAN CLASS="breadcrumb-item"
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><A HREF="index.html"
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>Common Lisp Nova Spec</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="23_Reader.html"
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>23. Reader</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="23_2_Reader_Dictionary.html"
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>23.2 Reader Dictionary</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="v_read-suppress.html"
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>*read-suppress*</A
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></SPAN
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></DIV
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><DIV CLASS="apropos"
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><DIV CLASS="apropos-io"
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><A HREF="v_read-eval.html" CLASS="prev"
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>←</A
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><SPAN ID="apropos-label"
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>Apropos </SPAN
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><INPUT ID="apropos" AUTOFOCUS="AUTOFOCUS" PLACEHOLDER="Type here to search" ONINPUT="aproposInput(this);" ONKEYUP="aproposKeyup(event);" ONCHANGE="aproposChange(this);" ONFOCUS="aproposFocus(this);" ONFOCUSOUT="aproposFocusout(this);"
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><A HREF="v_readtable.html" CLASS="next"
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>→</A
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></DIV
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><DIV ID="apropos-res"
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></DIV
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></DIV
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></DIV
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><DIV CLASS="matter"
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><DIV CLASS="com"
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><DIV CLASS="begincom"
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><HR
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><TABLE WIDTH="100%" CELLSPACING="0" CELLPADDING="0"
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><TR
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><TD ALIGN="LEFT" VALIGN="BASELINE" WIDTH="100%" CLASS="name"
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><SPAN CLASS="idx" DATA-KIND="idxref" DATA-TERM="*read-suppress*"
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></SPAN
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><SPAN CLASS="cmsy"
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>*</SPAN
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><B
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>read-suppress</B
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><SPAN CLASS="cmsy"
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>*</SPAN
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></TD
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><TD ALIGN="RIGHT" VALIGN="BASELINE" WIDTH="0" NOWRAP="NOWRAP" CLASS="ftype"
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><I
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>Variable</I
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></TD
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></TR
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></TABLE
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><HR
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></DIV
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><UL CLASS="subtoc"
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></UL
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><DL
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><DT
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><B
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>Value Type</B
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></DT
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><DD
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><P CLASS="j"
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>a <A HREF="26_1_Glossary.html#generalized_boolean"
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><EM CLASS="term"
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>generalized boolean</EM
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></A
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>.</P
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></DD
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><DT
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><B
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>Initial Value</B
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></DT
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><DD
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><P CLASS="j"
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><A HREF="26_1_Glossary.html#false"
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><EM CLASS="term"
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>false</EM
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></A
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>.</P
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></DD
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><DT
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><B
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>Description</B
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></DT
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><DD
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><P CLASS="j"
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>This variable is intended primarily to support the operation of the read-time conditional notations <CODE CLASS="f"
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>#+</CODE
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> and <CODE CLASS="f"
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>#-</CODE
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>. It is important for the <A HREF="26_1_Glossary.html#reader_macro"
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><EM CLASS="term"
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>reader macros</EM
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></A
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> which implement these notations to be able to skip over the printed representation of an <A HREF="26_1_Glossary.html#expression"
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><EM CLASS="term"
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>expression</EM
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></A
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> despite the possibility that the syntax of the skipped <A HREF="26_1_Glossary.html#expression"
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><EM CLASS="term"
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>expression</EM
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></A
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> may not be entirely valid for the current implementation, since <CODE CLASS="f"
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>#+</CODE
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> and <CODE CLASS="f"
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>#-</CODE
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> exist in order to allow the same program to be shared among several Lisp implementations (including dialects other than Common Lisp) despite small incompatibilities of syntax. </P
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><P CLASS="j"
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>If it is <A HREF="26_1_Glossary.html#false"
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><EM CLASS="term"
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>false</EM
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></A
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>, the <A HREF="26_1_Glossary.html#Lisp_reader"
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><EM CLASS="term"
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>Lisp reader</EM
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></A
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> operates normally. </P
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><P CLASS="j"
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>If the <A HREF="26_1_Glossary.html#value"
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><EM CLASS="term"
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>value</EM
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></A
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> of <A HREF="v_read-suppress.html" CLASS="misc"
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><B
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>*read-suppress*</B
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></A
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> is <A HREF="26_1_Glossary.html#true"
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><EM CLASS="term"
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>true</EM
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></A
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>, <A HREF="f_read.html" CLASS="funref"
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><B
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>read</B
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></A
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>, <A HREF="f_read.html" CLASS="funref"
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><B
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>read-preserving-whitespace</B
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></A
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>, <A HREF="f_read-delimited-list.html" CLASS="funref"
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><B
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>read-delimited-list</B
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></A
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>, and <A HREF="f_read-from-string.html" CLASS="funref"
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><B
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>read-from-string</B
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></A
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> all return a <A HREF="26_1_Glossary.html#primary_value"
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><EM CLASS="term"
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>primary value</EM
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></A
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> of <SPAN CLASS="misc"
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><B
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>nil</B
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></SPAN
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> when they complete successfully; however, they continue to parse the representation of an <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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> in the normal way, in order to skip over the <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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>, and continue to indicate <A HREF="26_1_Glossary.html#end_of_file"
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><EM CLASS="term"
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>end of file</EM
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></A
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> in the normal way. Except as noted below, any <A HREF="26_1_Glossary.html#standardized"
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><EM CLASS="term"
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>standardized</EM
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></A
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> <A HREF="26_1_Glossary.html#reader_macro"
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><EM CLASS="term"
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>reader macro</EM
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></A
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><SPAN CLASS="meaning"
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><SUB CLASS="sub"
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><SPAN CLASS="cmr"
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>2</SPAN
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></SUB
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></SPAN
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> that is defined to <A HREF="26_1_Glossary.html#read"
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><EM CLASS="term"
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>read</EM
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></A
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><SPAN CLASS="meaning"
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><SUB CLASS="sub"
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><SPAN CLASS="cmr"
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>2</SPAN
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></SUB
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></SPAN
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> a following <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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> or <A HREF="26_1_Glossary.html#token"
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><EM CLASS="term"
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>token</EM
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></A
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> will do so, but not signal an error if the <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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> read is not of an appropriate type or syntax. The <A HREF="26_1_Glossary.html#standard_syntax"
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><EM CLASS="term"
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>standard syntax</EM
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></A
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> and its associated <A HREF="26_1_Glossary.html#reader_macro"
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><EM CLASS="term"
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>reader macros</EM
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></A
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> will not construct any new <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>objects</EM
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></A
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> (<I CLASS="i"
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><I
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>e.g.</I
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></I
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>, when reading the representation of a <A HREF="26_1_Glossary.html#symbol"
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><EM CLASS="term"
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>symbol</EM
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></A
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>, no <A HREF="26_1_Glossary.html#symbol"
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><EM CLASS="term"
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>symbol</EM
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></A
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> will be constructed or interned).</P
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><DL
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><DT
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><SPAN CLASS="cmr"
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>Extended</SPAN
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> <SPAN CLASS="cmr"
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>tokens</SPAN
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></DT
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><DD
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><P CLASS="j"
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>All extended tokens are completely uninterpreted. Errors such as those that might otherwise be signaled due to detection of invalid <A HREF="26_1_Glossary.html#potential_number"
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><EM CLASS="term"
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>potential numbers</EM
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></A
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>, invalid patterns of <A HREF="26_1_Glossary.html#package_marker"
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><EM CLASS="term"
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>package markers</EM
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></A
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>, and invalid uses of the <A HREF="26_1_Glossary.html#dot"
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><EM CLASS="term"
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>dot</EM
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></A
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> character are suppressed.</P
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></DD
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><DT
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><SPAN CLASS="cmr"
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>Dispatching</SPAN
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> <SPAN CLASS="cmr"
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>macro</SPAN
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> <SPAN CLASS="cmr"
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>characters</SPAN
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> <SPAN CLASS="cmr"
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>(including</SPAN
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> <A HREF="26_1_Glossary.html#sharpsign"
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><EM CLASS="term"
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>sharpsign</EM
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></A
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><SPAN CLASS="cmr"
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>)</SPAN
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></DT
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><DD
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><P CLASS="j"
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><A HREF="26_1_Glossary.html#dispatching_macro_character"
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><EM CLASS="term"
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>Dispatching macro characters</EM
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></A
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> continue to parse an infix numerical argument, and invoke the dispatch function. The <A HREF="26_1_Glossary.html#standardized"
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><EM CLASS="term"
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>standardized</EM
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></A
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> <A HREF="26_1_Glossary.html#sharpsign"
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><EM CLASS="term"
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>sharpsign</EM
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></A
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> <A HREF="26_1_Glossary.html#reader_macro"
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><EM CLASS="term"
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>reader macros</EM
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></A
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> do not enforce any constraints on either the presence of or the value of the numerical argument.</P
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></DD
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><DT
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><SPAN CLASS="cmtt"
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>#=</SPAN
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></DT
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><DD
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><P CLASS="j"
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>The <CODE CLASS="f"
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>#=</CODE
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> notation is totally ignored. It does not read a following <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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>. It produces no <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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>, but is treated as <A HREF="26_1_Glossary.html#whitespace"
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><EM CLASS="term"
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>whitespace</EM
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></A
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><SPAN CLASS="meaning"
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><SUB CLASS="sub"
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><SPAN CLASS="cmr"
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>2</SPAN
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></SUB
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></SPAN
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>.</P
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></DD
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><DT
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><SPAN CLASS="cmtt"
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>##</SPAN
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></DT
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><DD
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><P CLASS="j"
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>The <CODE CLASS="f"
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>##</CODE
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> notation always produces <SPAN CLASS="misc"
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><B
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>nil</B
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></SPAN
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>.</P
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></DD
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></DL
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><P CLASS="j"
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>No matter what the <A HREF="26_1_Glossary.html#value"
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><EM CLASS="term"
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>value</EM
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></A
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> of <A HREF="v_read-suppress.html" CLASS="misc"
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><B
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>*read-suppress*</B
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></A
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>, parentheses still continue to delimit and construct <A HREF="26_1_Glossary.html#list"
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><EM CLASS="term"
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>lists</EM
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></A
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>; the <CODE CLASS="f"
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>#(</CODE
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> notation continues to delimit <A HREF="26_1_Glossary.html#vector"
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><EM CLASS="term"
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>vectors</EM
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></A
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>; and comments, <A HREF="26_1_Glossary.html#string"
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><EM CLASS="term"
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>strings</EM
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></A
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>, and the <A HREF="26_1_Glossary.html#single-quote"
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><EM CLASS="term"
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>single-quote</EM
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></A
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> and <A HREF="26_1_Glossary.html#backquote"
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><EM CLASS="term"
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>backquote</EM
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></A
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> notations continue to be interpreted properly. Such situations as <CODE CLASS="f"
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>')</CODE
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>, <CODE CLASS="f"
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>#<</CODE
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>, <CODE CLASS="f"
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>#)</CODE
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>, and <CODE CLASS="f"
|
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>#<SPAN CLASS="cmsy"
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>⟨</SPAN
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><I
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>Space</I
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><SPAN CLASS="cmsy"
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>⟩</SPAN
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></CODE
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> continue to signal errors.</P
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></DD
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><DT
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><B
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>Examples</B
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></DT
|
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><DD
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><PRE CLASS="screen"
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> (let ((*read-suppress* t))
|
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(mapcar #'read-from-string
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'("#(foo bar baz)" "#P(:type :lisp)" "#c1.2"
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"#.(PRINT 'FOO)" "#3AHELLO" "#S(INTEGER)"
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"#*ABC" "#\GARBAGE" "#RALPHA" "#3R444")))
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<SPAN CLASS="cmsy"
|
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><SPAN CLASS="arrow"
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>→</SPAN
|
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></SPAN
|
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> (NIL NIL NIL NIL NIL NIL NIL NIL NIL NIL)</PRE
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></DD
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><DT
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><B
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>See Also</B
|
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></DT
|
||
|
><DD
|
||
|
><P CLASS="j"
|
||
|
><A HREF="f_read.html" CLASS="funref"
|
||
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><B
|
||
|
>read</B
|
||
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></A
|
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>, Chapter 2 (Syntax)</P
|
||
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></DD
|
||
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><DT
|
||
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><B
|
||
|
>Notes</B
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></DT
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><DD
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><P CLASS="j"
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><A HREF="26_1_Glossary.html#programmer"
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><EM CLASS="term"
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>Programmers</EM
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></A
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> and <A HREF="26_1_Glossary.html#implementation"
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><EM CLASS="term"
|
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>implementations</EM
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></A
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> that define additional <A HREF="26_1_Glossary.html#macro_character"
|
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><EM CLASS="term"
|
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>macro characters</EM
|
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></A
|
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> are strongly encouraged to make them respect <A HREF="v_read-suppress.html" CLASS="varref"
|
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><B
|
||
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>*read-suppress*</B
|
||
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></A
|
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> just as <A HREF="26_1_Glossary.html#standardized"
|
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><EM CLASS="term"
|
||
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>standardized</EM
|
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></A
|
||
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> <A HREF="26_1_Glossary.html#macro_character"
|
||
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><EM CLASS="term"
|
||
|
>macro characters</EM
|
||
|
></A
|
||
|
> do. That is, when the <A HREF="26_1_Glossary.html#value"
|
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><EM CLASS="term"
|
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>value</EM
|
||
|
></A
|
||
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> of <A HREF="v_read-suppress.html" CLASS="misc"
|
||
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><B
|
||
|
>*read-suppress*</B
|
||
|
></A
|
||
|
> is <A HREF="26_1_Glossary.html#true"
|
||
|
><EM CLASS="term"
|
||
|
>true</EM
|
||
|
></A
|
||
|
>, they should ignore type errors when reading a following <A HREF="26_1_Glossary.html#object"
|
||
|
><EM CLASS="term"
|
||
|
>object</EM
|
||
|
></A
|
||
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> and the <A HREF="26_1_Glossary.html#function"
|
||
|
><EM CLASS="term"
|
||
|
>functions</EM
|
||
|
></A
|
||
|
> that implement <A HREF="26_1_Glossary.html#dispatching_macro_character"
|
||
|
><EM CLASS="term"
|
||
|
>dispatching macro characters</EM
|
||
|
></A
|
||
|
> should tolerate <SPAN CLASS="misc"
|
||
|
><B
|
||
|
>nil</B
|
||
|
></SPAN
|
||
|
> as their infix <A HREF="26_1_Glossary.html#parameter"
|
||
|
><EM CLASS="term"
|
||
|
>parameter</EM
|
||
|
></A
|
||
|
> value even if a numeric value would ordinarily be required.</P
|
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